Video recording cameras, or camcorders, typically utilize a solid state imager. The imager generates an image signal which is processed to form a video signal for television viewing or recording. Typically a camcorder includes a viewing device, or viewfinder, for viewing the scene, which may additionally be utilized for reviewing recorded material. The recording section may utilize a magnetic tape recording medium, magnetic disk, or solid state memory. The complete camera and recorder may be battery powered, often by a rechargeable battery.
A typical camcorder is illustrated in FIG. 1, and may be considered to comprise the major functional blocks shown. A zoom lens 100 is provided to gather illumination from a scene, and form a focused image on an imaging device 205. The zoom lens 100, usually provides control of three parameters namely, focus 110, zoom or magnification 120, and iris or aperture 130. Control of these optical parameters are usually facilitated by physical movement of constituent parts within the lens. For example, the iris or lens opening may be provided by a multi-blade diaphragm, zoom and focus may be facilitated by the repositioning of internal lenses. Often such mechanical movements are provided by electrically powered motors, frequently servo controlled to provide automatic optimization of the controlled parameter.
Imaging device 205, may for example be a charge coupled device or CCD, depicted FIG. 1 as part of a video signal generator 200. The video signal generator processes signals received from the CCD to stabilize black and white levels therein, to automatically control white balance, and to pre-correct or gamma correct the generated video signal for cathode ray tube, CRT, viewing. In addition processing is provided to enhance picture sharpness and to provide servo control signals for coupling to the lens for focus and iris control.
The processed video signals are encoded by encoder 300, which produces a standard color signal for television viewing. In addition a video signal is generated for coupling to a viewfinder 50. Luminance and encoded color subcarrier signals are generated by the encoder and record processed by amplifier 505 which is coupled to heads on head drum 510.
Recorder 500 is depicted as a magnetic tape recorder, utilizing a rotating head assembly or drum 510 comprising, for example, record, replay and erase heads. A capstan 520 with pinch roller 530 is employed to move the recording medium. Recorder 500 is shown loaded and threaded with tape 504 withdrawn from tape cassette 501 by threading mechanism and motor 527. The cassette comprises a tape supply reel 502 and a take up reel 503. Head drum 510 is rotated by motor 515 and is synchronized with the video signal, similarly capstan 520 is rotated by motor 525 which is also synchronized with the video signal.
The luminance and coloring signals are processed by a record and play back amplifier 505 which generates signals for recording and reproduction by heads mounted on the periphery of head drum 510. Reproduced signals from amplifier 505 are coupled to encoder 300 for viewfinder viewing and for processing to form a standard TV signal. The camcorder is controlled by a microprocessor 400 which operates in conjunction with a recorder mechanism controller 560.
Audio signals are captured by a microphone 70 and amplified by amplifier 75. In addition amplifier 75 may generate an audio modulated signal for recording and include a demodulator for audio reproduction and output coupling.
Camcorder 10 is powered by a battery 600, which for example, may be a rechargeable type having a nickel cadmium structure. Typically camcorders may function as a recording camera, or a VCR play back device. Battery power consumption is greatest when recording, and increases further with frequency of zoom lens and iris operation. Often a record pause mode is provided which allows recording to be halted and resumed without a visible replay disturbance. However, this mode frequently provides only minimal power savings, since in order to provide rapid resumption of recording, the head drum motor and capstan pinch roller often remain powered.
It is desirable that camcorder power consumption be reduced, for example, to provide increased operating time with a specific battery size or chemistry. Reduced power consumption may also, for example, allow the use of physically smaller batteries yielding a smaller or lighter camcorder. Reduced power dissipation may also permit camcorder operation with non-rechargeable or other battery chemistries, for example alkaline cells.
Clearly electronic circuit changes may offer opportunities for power reduction. However, camcorder operating time may be unintentionally shortened by unwanted or inadvertent camcorder operation which drains the battery. Various indicators of unwanted or inadvertent operation are known, for example, application EP 0 649-251 determines unwanted operation by detecting excess motor servo perturbations together with the absence of a users eye from a viewfinder eyepiece. In camcorders which employ image stabilization it is known to detect excess motion, which may result from unwanted operation, by using the angular velocity, or acceleration sensor. For example in application EP 0 580 333 A2 when a swing sensor repeatedly exceeds a threshold value during a record mode the recording is terminated and the media rewound to a point where the excessive swinging was initially detected. Laid open Japanese patent application 61-189077, recites a system for power conservation during wanted, intentional camera operation during fixed or tripod mounting. Application 61-189077 employs an angular motion sensor to indicate a lack of camera motion during static, fixed or tripod mounted operation. The detected lack of motion causes the termination of power supply to an electronic viewfinder. However, the display tube heater remains energized to allow the rapid resumption of camera viewfinder usage.